A. Field of the Invention
The present invention relates to apparatus for remotely orienting the distant tip of a flexible borescope. More particularly, the invention relates to articulation structures for borescopes employing pull wires.
B. Discussion of Background Art
Borescopes are elongated optical devices capable of transmitting visual images to a remote observer. The devices are used to transmit images of objects near the distant end of the device to an observer at the near end of the device. This image transmitting capability permits an observer to perform a visual inspection of remote objects within the field of view of the far end of the device. Borescopes were first used to inspect the bores of guns, hence the name. Presently, bore-scopes are used to permit inspection of a large variety of objects located in remote, inaccessible or hazardous areas. Thus, they are used in such diverse applications as the inspection of turbine engines, human bodies, and nuclear reactors.
The first borescopes were essentially rigid, elongated tubular microscopes which employed a series of lenses to convey an image of an object in the field of view of a field lens at a remote end of the tube to an objective lens at the observer's end of the tube. Usually, means were also provided to illuminate the field of view of the borescope, as for example by a small lamp located near the remote end of the tube.
Most modern borescopes utilize flexible fiber-optic cables rather than lenses. The fiber-optic cables contain parallel bundles of fine transparent fibers, and transmit to one end of the cable an image of the area within the field of view of the opposite end of the cable.
Most fiber-optic borescopes have a flexible protective sheath covering the entire length of the cable. Typically, the sheath is made of a durable, abrasion resistant material such as woven metal. Also, most fiber-optic borescopes include within the sheath a second fiber-optic cable which is illuminated by a bright light source at the observer's end. The second cable transmits light to the remote end of the cable, which then illuminates the field of view of the imaging fiber-optic cable.
In a recent development in flexible borescopes, a solid state television camera is contained within a borescope tip, eliminating the need for a fiber-optic image cable. The solid state camera sensor consists of a silicon chip less than 1/8" in diameter and having an array of light sensitive elements, arranged in a matrix. These devices, referred to as Charge Coupled Devices ("CCD's"), are imbedded in a borescope tip and produce a video signal capable of forming an image of objects within the field of view of the CCD. The video signal is conducted by means of electrical wires within the borescope cable to a television monitor located at the observer's end of the cable.
The tips of some fiber-optic borescopes can be remotely manipulated by an observer at the viewing end of the borescope to position the axis of the imaging fiber-optic cable at a desired orientation, thereby bringing into its field of view a desired area of interest. These remotely manipulatable fiber-optic borescopes are referred to as articulated, articulating or articulateable borescopes. By applying tension to one or more flexible wires strung through the protective sheath and attached to a pivotable member near the remote end or head of the cable, the head may be tilted at an angle to the longitudinal axis of the cable. Such borescopes can have either one or two planes of articulation. The latter type permits aiming the head of the borescope to any point in a forward directed hemisphere (or larger portion of a sphere) centered around the head end of the cable.
A variety of structures permitting the bending of the remote end of an articulated conduit by an operator at the near end of the conduit have been disclosed. Examples of such articulation structures are disclosed in the following U.S. Pat. Nos.:
Stegeman, 2,424,064, July 15, 1947, Illuminating Device
Ulrich, 3,071,161, Jan. 1, 1963, Bidirectional Flexible Segmented Tube
Bazinet, 3,162,214, Dec. 22, 1964, Flexible Tubular Structures
Stokes, 3,190,286, June 22, 1965, Flexible Viewing Probe for Stokes Endoscopic Use
Maudinet, 3,301,588, Jan. 31, 1967, Remote Control Manipulation of Inaccessible Objects
Marie, 3,326,620, June 20, 1967, Linked Wave Transmitting System for Light Waves
Bazell, 3,572,325, Mar. 23, 1971, Flexible Endoscope Having Fluid Conduits and Control
Takahashi, 3,583,393, June 8, 1971, Bendable Tube Assembly
Takahashi, 3,669,098, June 13, 1972, Endotracheal Tube
Fukaumi, 3,799,151, Mar. 26, 1974, Controllably Bendable Tube of an Endoscope
Hosono, 3,998,216, Dec. 21, 1979, Bending Tube for Endoscope
Tanaka, 4,108,211, Aug. 22, 1978, Articulated, Four-Way Bendable Tube Structure
Hosono, 4,347,837, Sept. 7, 1982, Structure for Preventing the Breakage of End Portions of a Protective Covering for the Adjustable Bend Section of an Endoscope
Ouchi, 4,351,323, Sept. 28, 1982, Curvable Pipe Assembly in Endoscope
Sakuragi, 4,396,797, Aug. 2, 1983, Flexible Cable
Sheldon, 3,060,972, Oct. 30, 1962, Flexible Tube Structure
Siegmund, 4,290,421, Sept. 22, 1981, Fiberscope
Wentzell, 4,575,185, Mar. 11, 1986, System for a Fiber-Optic Cable for Remote Inspection of Internal Structure of a Nuclear Steam Generator
All of those articulation control structures disclosed in patents listed above which are useful for articulating flexible borescopes have a common characteristic; each of the structures employs pull wires anchored to the far end of the articulateable tube section, near the borescope tip. The wires run back through guides within the borescope cable, are longitudinally slidable within the guides, and terminate at a differential tension producing member operable by a user at the observation end of the borescope cable. A single pair of wires provides two-way articulateability in a single plane. By differentially varying the tension in the two control wires, the borescope tip can be tilted in either of two directions in a single plane. Two pairs of wires are required to provided articulateability in two perpendicular planes (four-way articulateability). The Siegmund patent discloses an improved articulation structure in which three longitudinally disposed pull wires spaced at 120 degree circumferential angles provided four-way articulateability.
Wentzell, in U.S. Pat. No. 4,575,185, Mar. 11, 1986, discloses the use of sealed, flexible chambers within a flexible tube assembly. The chambers contain fluids and are differentially pressurized to vary the buoyancy of the tube assembly in a liquid environment, thereby permitting the remote end of the tube to be bent in a desired direction. By this means, the aim point of a fiber optic inspection cable contained coaxially within the flexible tube assembly may be controlled when the assembly is inserted into a liquid filled chamber such as a nuclear steam generator.
The pull wires used by all general purpose borescope articulation structures disclosed in the prior art impose certain limitations on the performance capabilities of borescopes equipped with those articulation structures. For example, the friction between the pull wires and their enclosing guide tubes becomes troublesome when long borescope cables are required Also, the weight added to the borescope cable by the lengths of 2, 3 or 4 stout pull wires can make manipulation of long cables quite difficult. As a practical matter, the above cited problems with existing pull-wire borescope articulation structures imposes an upper limit on the length of practical articulating borescopes.
ln our U.S. patent application Ser. No. 926,357 filed Oct. 31, 1983, we disclosed novel borescope articulation methods and apparatus employing shape memory effect (SME) alloy actuating elements. The SME alloy actuator mechanisms disclosed in that patent application provide a highly effective means of overcoming the limitations of prior borescope articulators The present invention was conceived of to provide a novel borescope articulation mechanism particularly well adapted to incorporation into, and modification of, existing pull-wire borescopes.